Distillation of fatty acids, tall oil, and the like



Feb. 3, 1953 R. H. POTTS ET AL 2,627,500

DISTILLATION OF FATTY ACIDS, TALL OIL, AND THE LIKE Filed Dec. 15, 1947Ill w" N ,La

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Patented Feb. 3, 1953 DISTILLATION F FATTY ACIDS, TALL OIL, AND THE LIKERalph H. Potts, La Grange, and Roy N. Olson,

Chicago, 111., assignors to Armour and Company, Chicago, 111., acorporation of Illinois Application December 15, 1947, Serial No.791,857

9 Claims. (Cl. 202-46) This invention relates to the distillation offatty acids, tall oil, and the like.

In the distillation of fatty acids, tall oil and similar materials inwhich the product is adversely affected by decomposition at hightemperatures, it has heretofore been felt desirable to limit the amountof steam employed in the distillation of such products. The use of steamin somewhat larger amounts is desirable from the standpoint of reducingthe temperature differentials existing in the top and bottom portions ofthe fractionating or distillation tower and particularly for reducingthe temperature in the lower portion of the tower. However, the use ofsuch large amounts of steam has a disadvantage in that a substantialentrainment occurs. This entrainment in addition to the actual lossincurred, passes into the vacuum equipment, solidifies in thecondensers, resulting in costly shutdowns. For this reason, the quantityof steam has been restricted and in some cases dispensed withaltogether.

The following example illustrates the advantage in using larger amountsof injected steam and emphasizes the unfortunate limitation of steamrequired to avoid entrainment losses. Consider a system operating with afeed composed of 50% palmitic acid and 50% stearic acid, a pressure ofmm. at the top of the tower and 45 mm. at the base of the tower. Thevapor temperature at the top of the tower would then be the temperatureat which the vapor pressure of palmitic acid is 5 mm. or 385 F. Thetemperature at the base of the tower would be the temperaturecorresponding to a vapor pressure of stearic acid of 44 mm. or 514 F.

If we now consider a system in which the partial pressure of thepalmitic acid at the top of the tower is again 5 mm. but the totalpressure is 30 mm. the remaining 25 mm. being the result of theadmission of 5 mols of steam per mol of fatty acid then we will find aconsiderable difference in the conditions existing at the base of thetower even though the top tower temperature remains the same, i. e., 386F. The 20 fractionating trays can again be designed for a pressure dropof 2 mm. per tray and the total pressure existing at the base of thetower will be 70 mm. The partial pressure of the fatty acid vapor willbe /6 of 70 mm. or 11.6 mm., and the corresponding vapor temperature atthe base of the tower will be the temperature at which stearic acidexhibits a vapor pressure of 11.6 mm. or 450 F.

From the above it will be noted that the use of steam considerablyreduces the temperature required in the base of the tower and suchreduced temperature sharply reduces the thermal decomposition of theproduct and results in a much improved product.

It will be obvious from the foregoing that if some simple means can beprovided which will take care of the entrainment and prevent seriousentrainment losses while at the same time permitting the use of largeamounts of steam, a decided advance will have taken place. In the firstplace, a temperature difference existing between the top and bottom ofthe tower will be reduced, as in the example above, from F. to 64 F.This difference more nearly represents the difference that existsbetween the respective boiling points of palmitic and stearic acid andis not so dependent upon tower pressure as in the first instance. Thisshould provide for better fractionating conditions, as pressure changesdue to fractionating vacuum will not cause as much change in stillconditions. In the second place, the temperature existing in the base ofthe tower is 64 F. lower when usin steam, and consequently,decomposition is greatly reduced. v

An object of the present invention is to provide a process utilizing tothe full the use of steam in distillation while at the same timeovercoming entrainment losses. A further object is to provide a processin which thermo-compressor steam which is employed in reducing thepressure upon a tower is utilized for carrying any entrainment resultingfrom the use of steam in a distillation tower to a second tower in whichsuch entrainment is recovered. A still further object is to provide fora steam distillation tower a supply of steam employed in a steam ejectorpump for reducing the pressure in another tower, such steam beingutilized for the additional important purpose of carrying anyentrainment from the preceding tower to the tower into which the steamfrom such steam ejector pump is introduced. A still further object is toprovide a process employing the thermo-compression steam usedin onetower for steam distilling in another tower whereby entrainment lossesare reduced and hot-well losses of any entrainment past the condenserswill be eliminated. Other specific objects and advantages will appear asthe specification proceeds.

The invention is illustrated in connection with apparatus in which itmay be eifectively employed, in the accompanying drawing in which is setout a diagrammatic layout of such apparatus.

In the illustration given, itwill be noted that there are three towers.Tower I receives the incoming feed in line Ii] and the residue fromtower I passes from pipe II to tower 2 where fractional distillation iscarried out. Residue from tower 2 passes through line I2 into tower 3.It will be noted that a single casing provides towers 2 and 3 and thatthe two towers are separated by an imperforate wall It.

Tower I is employed for steam distillation and in the preferred processis employed mainly for stripping a relatively light vapor fractionfromthe feed material. Such a fraction is condensed in condenser I l and theliquid product is recovered through line I5.

cating with the condenser H5 is a vapor pipe I6 leading to a catch-allIT. A reflux line pipe I8. leads from the bottom of the catch-all I1 andreturns to an intermediate portion of tower I. A vapor pipe I9.leadsfrom the catch-all I'I to a barometric condenser 28; Communicatingwith the top of the barometric condenser is an ejector pump BI. Since.such apparatusfor maintaining. reduced pressure iswell known, a furtherdetailed description is believed unnecessary.

The feed material consisting of fatty. acids, tall oil or similar typesof material enters the stripping tower I through. line It and theunvaporized residue. passes downwardly and. flows through line H intotower 2 where it isfurther fractionated. The line II is provided with.an electrically"controlled valve 22 which in turn is controlled by alevel controlling electric mecha-. nism 23; Since suchlevel maintainingmechanism is wellknown in the. art, a detailed description-here isbelieved unnecessary.

In tower-2; vapors are condensed in the condenser Zlt and a secondliquidfraction drawn off through the. pipe 25. It will be understood that anumber of liquid fractions may be recovered from difierent portions ofthe tower. Leading from the condenser 2 is a vapor pipe 26 whichcommunicates with a steam ejector pump 27!. Steam is introduced into thepump 25. throughthe valve controlled line 28. Such a pump iseffective inreducing. the pressure within condenser 2d and tower 2. The steamdischarged through the pump. 2'I- is conducted by pipe to a heater tilin which the temperature of the steam may be raised. The steam is heatedby steam coils SI or by any other suitable. means. The reheated steamenters the bottom of tower I and is effective in the steam distilling ofthe product in that tower.

We have already referred to the withdrawal of residue from tower 2 andthe passing. of the same through pipe I2 into the lower tower 3, Thepipe I2 is provided with an electrically controlled valve 32 which inturn is controlled by an electrically operated level control device 33similar to the structure 23 employed in tower I. Heating coils for steamor other material. 35 may be employedin connection with tower 3. Ifdesired, the tower 3 may be left unheated and employed solely as anunheated flash drum. If desired, entrainment eliminators 35 may besupported in the upper portion of tower 3. A withdrawal pipe 35 forresidue is controlled by the electrically operated valve 51 which is inturn controlled by the electrical level maintaining device 38.

Communicating with the top of tower 3 is a vapor withdrawal pipe 39'leading to a condenser A reduced pressure. is. maintained by a structurewhichis wellzknown. and which will be briefly described. Communis.

40. A liquid fraction is recovered from the condenser through the pipe4L Communicating with the condenser 40 is a Vapor pipe 42 to which isconnected a two-stage steam ejector pump. Steam is introduced throughthe valve controlledpipe, 43 into the pump 434 and steam is alsointroduced through the valve controlled pipe 45 into the pump 46. Thesteam outlet from pump id communicates with pump $5 and the combinedoutput of steam passes through pipedl'into the reheater 53 where a steamcoil 99' may be used for raising the temperature of the steam. It willbe understood that any type of heating meansmay be employed for thispurpose.- Thesteam passes from the heater 48 into the lowerportion oftower 2.

As an example of the process, the following may be set out. A fatty acidcompounded mainly of palmitic and oleic acids was passed through feedline It into tower I; The top of tower I was maintained at a temperatureof 315 F. while the tower bottom was maintained at about 400 F. Tower 2had a toptemperature of 382 F. and a bottom temperature of 456 F. Tower3 hada top temperature of about 375 F. with the temperature of theliquid in the bottom being about 425 F.

The fraction recovered from tower I through pipe I5 consisting mainly ofan odoriferous materialwas withdrawn mainly for the purpose of removingthis constituent from the remaining material. The fraction, 2 recoveredfrom tower 2 through pipe 25 oonsistedlmainly of palmitic acidwhilefraction 3 from pipe 4| leading from tower 3, consisted mainlyofoleic acid. The residue through pipett was a heavy tarry material. Theproportions in the specific example were 5% in fraction I (odoriferousmaterial), 20%. in fraca tion 2 (palmitic), 55% in fraction 3 (oleic)and 20% in residue.

In the above specific example, lbs. of steam was introduced through pipel3, 600.1bs. through pipe d5 and 400 lbs. through pipeZB. Tower I had atop pressure of 40mm. of mercury. Tower 2 had a top pressure-of 30 mm.and abottom pressure of '70 mm. while tower 3 had a. pressure of 2 mm.Hg.

The heaters Btand it were efiectivelyemployed not only as steamreheaters but also as reboilers. They were effective in introducingadditional heat into the material being vaporized as well as in raisingthe temperatureof the incoming steam.

In the operation of the process as described above, it was found thatentrainment losses were nullified by carrying the entrainment throughthe medium of the thermo-ccmpressor steam back into the next tower sothat such entrainment materials were wholly recovered. Whetherentrainment was large or small was of little consequence because thematerialentrained was immediately subjected to a steam distillation inthe next tower. The processresultsin a saving of steam but moreimportant is the fact that the steam is employed, as a vehiclefor thereturn of entrained material so that it can be recovered. With the newprocess any desired large amount of steam may be employed with all theattendant advantages. which havev been described as flowing from suchuse while. at the same time the disadvantages heretofore followingtheuse of such large amounts of steam are eliminated.

The foregoing process involving fractional distillation or straightdistillation has been described in connection with fatty acids, tal-lacids, etc., for

the purpose of specifically illustrating the invention. It will beunderstood. that the invention is applicable for the treatment of fattyacid derivatives, such as their esters, alcohols, nitriles, amines, etc.The invention is particularly effective with fatty acids and suchderivatives having from 8 to 24 carbon atoms in their hydrocarbonradical. Broadly, the invention applies to all organic materials whosedistillation temperature is such that decomposition occurs or is likelyto occur in the range of the distillation temperatures. The invention isparticularly useful in the treating of such an organic material havingfrom 8 to 24 carbon atoms in its hydrocarbon radical.

While in the foregoing spec fication we have set out the process ingreat detail and in connection with apparatus which is described indetail, it will be understood that such details of steps and structuremay be varied widely by those skilled in the art without departing fromthe spirit of our invention.

We claim:

1. In a process for distilling an or anic material having from 8 to 24atoms in its hydrocarbon radical, the steps of maintaining at least twodistillation zones, passing material to be distilled into the first ofsaid zones, withdrawing vapors therefrom, passing material from saidfirst zone to the second zone, condensing vapors from said second zone,withdrawing a portion of the condensate, passing steam pa t said secondzone and in open communication with the condensing area thereof, andpassing said steam and material entrained therewith from said secondzone into said first zone.

2. In a process for the distillation of an organic material having from8 to 24 atoms in its hydrocarbon radical, the steps of maintaining atleast two distillation zones, passing material to be distilled into thefirst of said zones, withdrawing vapors therefrom, passing material fromsaid first zone to the second zone, condensing vapors from said secondzone, passing steam past said second zone and in open communication withthe condensing zone thereof, and introducing said steam with materialentrained therewith from said second zone into said first zone.

3. In a process for distilling an organic material having from 8 to 24carbon atoms in its hydrocarbon radical, the steps of steam distillingthe material to be distilled, withdrawing vapors therefrom, passingmaterial therefrom to a second distillation zone, condensing vapors fromsaid second zone, withdrawing a portion of the condensate, dischargingsteam past said zone and in open communication with the condensingportion of said second zone, and directing said discharged steamtogether with material entrained therewith into said first distillationzone.

4. In a process for distilling an organic material having from 8 to 24carbon atoms in its hydrocarbon radical, the steps of steam distillingthe material to be distilled, withdrawing vapors therefrom, passingunvaporized material therefrom to a second distillation zone, condensingvapors evolved from said second zone, discharging steam past said secondzone and in open communication with the condensing portion of saidsecond zone, reheating the discharged steam and introducing it into saidfirst distillation zone.

5. In a process for treating fatty acids and tall oil, the steps ofsubjecting the material to be distilled to a plurality of separatefractional distillation operations, condensing vapors from said separatedistillation operations, withdrawing a portion of the condensate,passing steam past one of said zones in open communication with thecondensing zone thereof, and introducing said steam and materialentrained thereby into a preceding distillation zone.

6. In a process for treating fatty acids and tall oil, the steps ofsubjecting the material to be distilled to a plurality of separatedistillation operations, condensing vapors from a plurality of saiddistillation operations, withdrawing a portion of the condensate,passing steam in a plurality of streams past said zones and in opencommunication with the condensing zone thereof, and passing each of saidsteam streams into preceding distillation zones.

7. In a process of the character set forth, the steps of steamdistilling the material to be distilled to strip the same of lightvapors, distilling the stripped material under reduced pressure,condensing vapors from said second zone, withdrawing condensate, passingsteam in a stream past the condensing zone of said second distillingzone and in open communication therewith, introducing said stream ofsteam into said first distillation zone, passing material from saidsecond zone into a third distillation zone of reduced pressure, passingsteam past the third distillation zone in open communication therewith,and introducing said second stream of steam into said seconddistillation zone.

8. In a process for treating an organic material having from 8 to 24carbon atoms in its hydrocarbon radical, the steps of subjecting saidmaterial to steam distillation, withdrawing and condensing vaporstherefrom, withdrawing condensate, passing unvaporized heated residuetherefrom to a second zone, condensing vapors from said second zone,passing steam in a stream past said second zone and in opencommunication with the condensing zone of said second distillation zone,and passing said steam together with material entrained therewith intosaid first mentioned zone.

9. In a process for treating a material stock selected from the groupconsisting of fatty acids and tall oil, the steps of subjecting saidstock to steam distillation, withdrawing and condensing vaporstherefrom, passing unvaporized heated residue therefrom to a secondzone, condensing vapors from said second zone, passing steam in a streampast said second distillation zone and in open communication with thecondensing zone of said second distillation zone, heating said stream ofsteam and passing the same into said first mentioned distillation zone.

RALPH I-I. PO'I'TS. ROY N. OLSON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date Re. 22,775 Potts July 30', 19462,161,798 Carter June 13 1939 2,164,593 Rector July 4, 1939 2,224,984Potts et a1. Dec. 17, 1940 2,361,411 Murphy Oct. 31, 1944 2,368,669 Leeet a1. Feb. 6, 1945 2,461,694 McCubbin et a1. Feb. 15, 1949

6. IN A PROCESS FOR TREATING FATTY ACIDS AND TALL OIL, THE STEPS OFSUBJECTING THE MATERIAL TO BE DISTILLED TO A PLURALITY OF SEPARATEDISTILLATION OPERATIONS, CONDENSING VAPORS FROM A PLURALITY OF SAIDDISTILLATION OPERATIONS, WITHDRAWING A PORTION OF THE CONDENSATE,PASSING STEAM IN A PLURALITY OF STREAMS PAST SAID ZONES AND IN OPENCOMMUNICATION WITH THE CONDENSING ZONE THEREOF, AND PASSING EACH OF SAIDSTEAM STREAMS INTO PRECEDING DISTILLATION ZONES.